In the steam generator arts, one consideration is corrosion of steel piping or other steel components that come into contact with steam. Corrosion problems are enhanced at higher steam temperatures. A known approach for reducing corrosion is the oxygen water treatment (OWT). See, e.g. Steam: Its Generation and Use, 41st edition, edited by J. B. Kitto and S. C. Stultz (The Babcock & Wilcox Company, Barberton, Ohio, USA© 2005), the text of which is hereby incorporated by reference as though fully set forth herein in its entirety.
A problem with the OWT process manifests at higher temperatures, which increases oxide growth on the inner surfaces of the superheater and reheater pendants from steam oxidation. When the oxide becomes sufficiently thick, the outer layer of the oxide tends to exfoliate in large flakes from the tube inner diameter (ID) surfaces during cooling. OWT reduces the critical thickness for oxide exfoliation. The exfoliant can accumulate in the tube bends and plug the steam flow path during the following boiler restart. The pluggage reduces the cooling effect from steam and can lead to overheating tube failures.
Current methods of managing the problem of oxide exfoliation in steam generators that employ OWT include: (1) upgrading the superheater and reheater pendants to more oxidation-resistant alloys; (2) more frequent shutdowns of the boilers, followed by steam blows to clear the exfoliant from the tube loops before restart; (3) using X-ray and/or a magnet to determine the amount of pluggage in the tube bends, followed by cutting substantially blocked tube loops to clear the exfoliant; and (4) processing the tube ID to increase the oxidation resistance of the tube surface. Two or more of these four solutions are sometimes employed together to deal with the oxide exfoliation problem. Implementation of any of these four methods is expensive and time consuming. Methods (2) and (3) are focused on physical removal of the oxide exfoliant accumulated in the tube loops, while methods (1) and (4) upgrade tube surface chemistry to combat excessive oxidation.